For lithium ion secondary batteries, which are excellent in energy density and are widely used for mobile devices, those using a laminated film for the package member are put in practical use because of their lighter weight and high energy density, the manufacturability of batteries with a very thin shape, etc.
In the battery thus using a laminated film as the package member, an electrolyte solution and a polymer compound are used as the electrolyte for the purposes of resistance to liquid leakage etc., and such a battery is known as a polymer battery. Among them, a battery using a gel electrolyte in what is called a gel form in which an electrolyte solution is retained in a polymer compound is widely used.
In the polymer battery, the shape variability is greatly improved by using an aluminum laminated film for the package member, but on the other hand, the strength may be insufficient and deformation is likely to occur when strong force is applied due to misuse.
In this case, although there is no problem in the case of being covered with a strong outer pack, the outer pack is becoming simpler with the recent requirement for higher capacities, and when the deformation is large, the battery is likely to experience a short circuit inside and may not function as a battery.
In this regard, in Patent Literature 1, it is proposed to mix particles of alumina or the like in the gel electrolyte to improve the strength of the gel.